Optical peristaltic pumping with optical traps

ABSTRACT

A method of use for holographic optical traps or gradients in which repetitive cycling of a small number of appropriately designed arrays of traps are used for general and very complex manipulations of particles and volumes of matter. Material transport results from a process resembling peristaltic pumping, with the sequence of holographically-defined trapping or holding manifolds resembling the states of a physical peristaltic pump.

This invention was made with U.S. Government support under Contract No.DMR-9730189 awarded by the National Science Foundation, and through theMRSEC Program of the National Science Foundation under Award No.DMR-9880595. The U.S. Government also has certain rights to theinvention pursuant to these contracts and awards. This application is acontinuation of U.S. patent application Ser. No. 10/651,370, filed Aug.29, 2003, which is a continuation of U.S. patent application Ser. No.09/875,812, filed Jun. 6, 2001, now U.S. Pat. No. 6,639,208.

FIELD OF THE INVENTION

The present invention is directed generally to a method and apparatusfor controlling and manipulating small particles, a movable mass or adeformable structure. More particularly, the present invention isdirected to a method and apparatus for using holographic optical trapsto control and manipulate particles and volumes of matter in bothgeneral and complex ways.

BACKGROUND OF THE INVENTION

Optical traps use optical gradient forces to trap, most preferably,micrometer-scale volumes of matter in both two and three dimensions. Aholographic form of optical trap can use a computer-generateddiffractive optical element to create large numbers of optical trapsfrom a single laser beam. These traps can be arranged in any desiredconfiguration dependent on the need at hand.

Although systems are known to move particles precisely and with arelatively high degree of confidence, conventional systems require aseparate hologram to be projected for each discrete step of a particle'smotion. Computing multiple holograms can be very time consuming andrequires substantial computational effort. Furthermore,computer-addressable projection systems required to implement suchcomputer-generated optical traps or other dynamic optical trap systems,such as scanned optical tweezers, tend to be prohibitively expensive.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide an improved methodfor manipulating particles and volumes of matter in both general andcomplex methods.

It is an additional object of the invention to provide an improvedmethod for moving particles along a predetermined path with a highdegree of accuracy and confidence.

It is still another object of the invention to provide a method formanipulating particles and volumes of matter which removes thecomputational burden of achieving complex rearrangements.

In accordance with the above objects, projecting a time varying sequenceof such trap patterns makes possible dynamic reconfiguration of traps,with each new pattern updating the position of each trap by a distancesmall enough that particles trapped in the original pattern naturallyfall into a corresponding trap in the next. The present inventiontherefore offers a method for accomplishing complex rearrangements ofmatter by cycling through a small number of precalculated holographicoptical trap patterns. The cycling can be performed mechanically,removing both computational complexity and the expense of a fullygeneral holographic optical trap system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an individual particle being trapped in an optical trapwithin a manifold of optical traps, wherein the manifold's position isrepresented by a dashed line;

FIG. 2 shows the transfer of an individual particle from a manifold oftraps in a first pattern to a manifold of traps in a second pattern;

FIGS. 3A-3D shows the operative action of an optical peristalsis method;

FIG. 4 shows the use of parallel linear manifolds of optical traps fortransferring particles along a linear trajectory normal to themanifolds;

FIG. 5A shows curved manifolds directing particles from the periphery ofthe pattern towards the centers of curvature; and FIG. 5B schematicallyshows how the pattern described in FIG. 5A can sweep particles into achannel;

FIG. 6A shows nonuniformly curved manifolds used to divide a flow ofparticles into two separate flows; and FIG. 6B shows nonuniformly curvedmanifolds to mix two separate flows into a single, larger flow;

FIG. 7A shows a plurality of concentric manifolds transporting particlesout of a region; and FIG. 7B shows a plurality of concentric manifoldstransporting particles into a region;

FIG. 8 is a representation of two particles moving in response to anexternally applied field and an optical peristalsis pattern;

FIG. 9 shows two stages of optical fractionation, with particles of afirst type transported to the right and particles of a second type aretransported to the left;

FIG. 10 is a representation of the implementation of optical peristalsisusing dynamical holographic optical traps;

FIG. 11 shows a dynamic holographic optical trap system using atransmission-mode computer-addressed spatial light modulator in anoptical train;

FIG. 12 shows the mechanical cycling of a sequence of staticcomputer-generated diffractive optical elements;

FIG. 13 is a representation of a mechanically cycled optical peristalsissystem using transmissive computer-generated diffractive opticalelements arranged on the periphery of a disc;

FIG. 14 shows a plurality of manifolds of optical traps trapping anextended object and rotating the object; and

FIG. 15 shows the use of manifolds of optical traps trapping an extendeddeformable object.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Optical peristalsis involves the use of a sequence of pre-calculatedholograms projected over time to implement complex redistributions oflarge numbers of particles over large or selected areas. A key aspect ofthe invention of optical peristalsis is the non-specific transfer ofparticles from one manifold of optical traps in a given pattern to thenext pattern through the intercession or application of at least twointermediate patterns. The term “pattern” is meant to encompass at leastone manifold. FIG. 1 shows a typical manifold 20 of optical traps 24arranged in a straight line. Each of the traps 24 is capable of trappinga particle 22 of interest, and the traps 24 are spaced relative to eachother so that the particle 22 is unlikely to pass through the manifold20 without falling into an available one of the traps 24 or beingblocked by particles already in the trap 24. The particle 22 is drawn asa sphere, but could just as easily be irregularly shaped, or even muchlarger than the separation between the traps 24.

Operation of the optical peristalsis method proceeds by extinguishingthe manifold 20 of the traps 24 which frees the particle 22 to move. Ifanother pattern of the traps 24 is illuminated sufficiently nearby, thenthe particle 22 will be trapped by one (or more) of the traps 24 in thenew pattern. In the illustrated case of FIGS. 3A-3D a pattern includestwo of the manifolds 20 at line 23 and 25. However, the next patterncould include only one of the manifolds, along line 27 for example. Ineffect, the particle 22 is thereby transferred from one of the manifolds20 of the traps 24 in the first pattern 26 to another one of themanifolds 20 in a second pattern 28. This process is in its simplistform depicted in FIG. 2, and shown more generally in FIGS. 3A-3D. Toeffect the transfer of the particle 22, the first pattern 26 can beextinguished first; and then the second pattern 28 is illuminated,provided the interval between the two patterns 26 and 28 is short enoughto prevent the trapped particle 22 from “wandering off” (out of theoptical gradient) before it can be captured by the next, nearestavailable trap 24. Illuminating the second pattern 28 beforeextinguishing the first pattern 26 also is another operative embodiment,albeit, more complicated to implement.

A pattern of the traps can therefore include one or more of themanifolds 20 of discrete the traps 24, such as discrete tweezers in oneembodiment of the invention. Each of the manifolds 20 can includeseveral of the traps 24 arranged along a one-dimensional curve or line,as shown schematically in FIG. 1, or also on a two-dimensional surface,or within a three-dimensional volume. The notion of a trapping patternconsisting of a collection of the manifolds 20 is useful for visualizingthe process of optical peristalsis.

FIG. 3A shows in further detail one of the particles 22 trapped on onemanifold 20 of a particular pattern, labeled as the first pattern 26.The first pattern comprises two manifolds 50 and 56. The positions oftrapping the manifolds 52 and 54 in the second extinguished pattern 28(only one manifold for this pattern) and a third extinguished pattern 30(only one manifold) are also shown. In the first time step, only thefirst pattern 26 is illuminated. In the next time step represented inFIG. 3B, the first pattern 26 is extinguished and the second pattern 28is illuminated. This action transfers the particle 22 from the firstmanifold 50 of the first pattern 26 to the nearby manifold 52 of thesecond pattern 28. In the next time incremental step shown in FIG. 3C,the second pattern 28 is extinguished and the third pattern 30 isilluminated, thereby transferring the particle 22 again and this time toa manifold 54 on the third pattern 30. In the final time step as shownin FIG. 3D, the third pattern 30 is extinguished and the first pattern26 is illuminated once again. This transfers the particle 22 to thefirst pattern 26 on the next manifold 56. Optical peristalsis thereforearises from deterministically transferring the particle 22 from one ofthe manifolds 20 on a pattern of the optical traps to another of themanifolds 20 on the same second pattern 28 by cycling through a sequenceof intermediate patterns.

In a most preferred embodiment of the invention, a minimum of three ofthe patterns 26, 28 and 30 are needed to advance the particle 22deterministically from the one manifold 50 on a trapping pattern to thenext manifold 52. If only two of the equally spaced patterns 26 and 28were used, the particle 22 could have a substantial probability ofeither advancing to the next manifold 52 or returning to the initialmanifold 50. In other embodiments, more than the three patterns 26, 28and 30 can be used to transfer a particle 22 in a particular direction.Methods for illuminating and extinguishing the individual manifolds 20of optical traps 24 are well understood in the art.

Repeatedly cycling through the first, second and third patterns 26, 28and 30, respectively, tends to move the particles 22 from left to rightin the arrangement described in FIG. 3. Reversing the sequence woulddrive them right to left. More extensive patterns consisting of more ofthe manifolds 20 thus can be used to transfer the particles 22 back andforth over the entire field of view of the holographic optical trapsystem.

There are a variety of ways in which optical peristalsis can be used toeffect useful rearrangements of collections of the particles 22. Thesemethods include modifying the shapes of the manifolds 20 within apattern of the traps 24 by continuous curves. Although a single patternis described in detail herein, additional intermediate patterns requiredfor transfer between the manifolds 20 would be easily understood andrecognized by those skilled in the art. In the examples describedherein, the direction of particle flow will be indicated by overlaidarrows.

FIG. 4 shows one of the patterns 26 from a linear optical peristalticpump 33. Two or more patterns (not shown) interleaved between themanifolds 20 of this pattern 26 can be activated in sequence to driveone or more trapped particles 22 from left to right. Reversing thesequence transfers the particles 22 from right to left. This pattern,and all of the patterns to be described herein, can be oriented in anydesired direction

FIGS. 5A and 5B show that patterns consisting of the curved manifolds 20can be used to concentrate a flow of particles. Conversely, running thesame sequence backwards disperses the particles 22. This capabilitywould be useful for directing the particles 22 out of an open region andinto a confined region, such as a reservoir. It is not necessary thatthe individual manifolds 20 have equal curvature, and varying thecurvature can be useful in particular situations. For instance, a linearpumping pattern can be used to sweep the particles 22 into a focusingpattern. The individual spacings between the manifolds 20 also do nothave to be equal. Regions of a pattern with more closely spaced forms ofthe manifolds 20 tend to transfer particles 22 more slowly than regionswith more widely spaced ones of the manifolds 20. The densely packedmanifolds 20 tend to concentrate the particles 22 along the direction ofmotion, while widely spaced manifolds 20 can be used to spread them out.This approach could be particularly beneficial in a focusing pattern toavoid overcrowding the particles 22 as they are concentrated.

The distribution and density of the traps 24 along a manifold also canbe used to control the flow of the particles 22 between the manifolds20. For instance, the traps 24 may be evenly spaced along each of themanifolds 20 and aligned simply from the one manifold 20 to the next andfrom one pattern to the next. In other embodiments, more complicatedarrangements of the traps 24 along the manifolds 20 and between patternscan have uses for controlling the flow of particles 22 along a sequenceof patterns. Similarly, varying the intensity, as well as the spacing,of individual traps 24 along the manifolds 20 in a pattern can haveuseful applications for controlling transport of the particles 22.

The tendency of the shaped manifolds 20 to direct the flow of theparticles 22 can also be used to direct the particles 22 into anydesired complicated pattern. The example shown in FIG. 6A shows theshaped manifolds 20 directing one flow of the particles 22 into two.When run in reverse, such a pattern could be used to combine two (ormore) flows into one. Although this may not be as efficient, because theparticles 22 from one flow will remain near others from the same flowonce the manifolds 20 merge, the methodology can still be used toadvantage.

The example shown in FIG. of 6B shows one way to induce mixing of theparticles 22 from combined flows. This example shows that the manifolds20 in a pattern need not be disjoint. The patterns in this systemsinclude a crossed form of the manifolds 20 in the mixing regions. Suchcrossings can be useful for exchanging the particles 22 between theinitially distinct flows. Crossing or otherwise intersecting the simplemanifolds 20 to form more complex manifolds 20 introduces aprobabilistic element into optical peristalsis. The particles 22 aregiven a choice of directions to travel near each crossing. Whichdirection the individual particles 22 choose to follow is determined byrandom thermal forces at the hand-off from one pattern to the next in asequence. Hence, the crossings shown in FIG. 6B can lead to a certaindegree of mixing.

A pattern of closed form of the manifolds 20, such as the example shownin FIGS. 7A and 7B, can transport the particles 22 into or out of aregion. Whether the pattern compacts or rarefies the region depends onthe order in which the sequence of patterns is projected. The example inFIG. 7A is useful for clearing the particles 22 out of a region, such asto facilitate tests on the suspending fluid or measurements on isolatedparticles 22. Such patterns need not be circular, nor need they beconfined to the plane. In principle, two-dimensional forms of themanifolds 20 in three-dimensional patterns can be useful for drawingmaterial into a volume, or pushing material out of a volume.

Additionally, it should be noted that competition between opticaltrapping and other external forces can have useful applications. Forexample, competition between optical trapping and other external forcescould be particularly useful in fractionating the particles 22 from adistribution. As an example, it is helpful to consider the particles 22entrained in a flow of surrounding fluid. Each of the particles 22 istransported by viscous drag in the local flow field {overscore(u)}({overscore (r)}) with a force {overscore (f)}=γ{overscore (u)}determined by its drag coefficient γ. For a sphere of radius α in afluid of viscosity η, the drag coefficient is given by γ=6πηα andincreases linearly with the particle's radius. A larger particle feels agreater force when held stationary against a flow than a smallerparticle. While the force due to viscous drag is one example of anexternal force, others such as those due to electric or magnetic fieldsalso would pertain in this embodiment described herein.

If the external force is weaker than the optical gradient force of agiven one of the optical traps 24, then the particle 22 beingtransported by optical peristalsis will move much as describedhereinbefore. If the external force is greater than the optical gradientforce of the optical trap 24, then optical peristalsis may only perturbthe motion of the particle 22 in the external field. In the idealizedexample shown in FIG. 8, one type of the particle 22 is more stronglyattracted to the optical traps 24 than it is driven by the externalfield. In the example shown in FIG. 8, a first particle 60 is moreamenable to trapping than a second particle 62 or is less stronglyinfluenced by the external field than the second particle 62. The firstparticle 60 is therefore transported by optical peristalsis and can becollected. The second particle 62 is more strongly driven by theexternal field and passes through the pattern of the traps 24, perhapsbeing diverted to a certain extent from its initial course.

The two types of the particles 60 and 62 in the example embodiment shownin FIG. 8 are distinguished either by their affinity for the opticaltraps 24, by their response to the external field, or both. Choosing thespatial distribution, strength, and other characteristics of the opticaltraps 24 in such a pattern makes fractionation of particles possible,with the selectivity determined by the particles' differing physicalcharacteristics.

The optical fractionation technique has a number of significantadvantages. Fractionation occurs along the direction of the appliedfield in electrophoresis. Optical fractionation can transport theselected fraction laterally. This means that optical fractionation canoperate continuously, rather than on one batch at a time. Becauseoptical fractionation relies on holographic optical trap technology, itcan be adapted readily to different fractionation problems.

For example, multiple stages of optical fractionation can be applied oneafter another using the same method and apparatus. Tuning each stage toextract a particular fraction of an initially mixed multicomponentsample then will separate the sample into each of its components,conveniently displacing the sorted components laterally away from theflow, and perhaps transporting them to channels or reservoirs usingtechniques previously described.

The example embodiment shown in FIG. 9 builds on a single fractionationstage by including a second stage of optical fractionation. The externalforce driving the particles 22 through the region is directed downward.A first pattern, labeled 80 in FIG. 9, selects particles of first type84 and moves them to the right, diverting, but not collecting particlesof second type 86. The second stage of fractionation, labeled portion82, can feature more intense or more closely spaced examples of thetraps 24 with the ability to divert particles 22 of the second type 86away from the external force. As shown, this second stage pattern 82transports to the left, still further enhancing the separation betweenthe fractions 84 and 86. Although the two stages of fractionation arepresented as conceptually separate, they could be implemented as asingle pattern of the optical trap manifolds 20. This process can alsobe generalized to include more stages and to incorporate transferringfractionated particles for collection.

As discussed above, optical peristalsis works by repetitively cyclingthrough a sequence of trapping patterns. The dynamic holographic systemsrepresented schematically in FIGS. 10 and 11 are a fully generalimplementation. In this case, a computer-addressed spatial lightmodulator 102 creates the configuration of laser beams 104 needed toimplement a given pattern of optical traps 114 by encoded the necessaryphase modulation onto the wavefront of an input laser beam 100. Inprinciple, such a system can implement any sequence of trappingpatterns, and thus any variant of optical peristalsis. In practice,however, the spatial light modulator 102 has physical limitations suchas spatial resolution which limit the complexity of the patterns whichthey encode. Also, such spatial light modulators 102 tend to be costly.

In the embodiment shown in FIG. 10, optical peristalsis can be performedwith the dynamical holographic optical traps 114, a typicalimplementation of which is shown. An input laser beam 100 is reflectedoff the surface of the computer-addressed spatial light modulator (SLM)102. The SLM 102 encodes a computer-generated pattern of phase shiftsonto the wavefront of the beam 100, thereby splitting it into one ormore separate laser beams 104, each emanating from point 107 in thecenter of the face of the SLM 102. Lenses 108 and 110 relay each ofthese laser beams 104 to the conjugate point 112 at the center of theback aperture of a high NA objective lens 112. This objective lens 112focuses each of the laser beams 104 into a separate optical trap 114,only one of which is shown in FIG. 10 for clarity. A dichroic mirror 116reflects trapping light into the objective lens 112 while allowingimaging illumination to pass through, thereby permitting images to beformed of the particles being trapped. Updating the phase modulationencoded by the SLM 102 causes a new pattern of the traps 114 to appear.Cycling through a sequence of optical peristalsis patterns in thismanner implements the corresponding optical peristalsis process. Becausethis system can be reconfigured in software, it represents a generalimplementation of optical peristalsis. In another embodiment shown inFIG. 11, the dynamic holographic optical trap system uses atransmission-mode computer-addressed spatial light modulator 200 in anoptical train otherwise similar to that in FIG. 10. This system also canbe used to implement optical peristalsis by cycling through a sequenceof trapping patterns.

Implementing optical peristalsis does not necessarily require thegenerality and reconfigurability offered by a dynamic holographicoptical trap system. Instead, implementing optical peristalsispreferably uses a holographic optical trap system capable of projectinga (small) sequence of otherwise static patterns. In its simplestpreferred form, optical peristalsis can be implemented by mechanicallycycling through a sequence of phase patterns to implement acorresponding sequence of holographic optical trapping patterns. Oneparticularly useful embodiment appears in FIG. 12. As shown in FIG. 12,the phase patterns needed to implement a particular optical peristalsisprocess are encoded in the surface relief of reflective diffractiveoptical elements 304, 306 and 308. These elements 304, 306, and 308 aremounted on the face of a prism 300, and each is rotated into place by amotor 302. Reversing the motor's rotation reverses the sequence ofpatterns and thus the direction of optical peristalsis. Rotating theprism 300 with the motor 302 orients each of the patterns in the inputlaser beam so that the diffracted beams created by the aligneddiffractive optical elements 304, 306 and 308 all create optical traps114. Stepping the motor 302 through each of the patterns in sequenceimplements optical peristalsis. Prisms with more than three patterns canbe employed, if desired or necessary.

Mounting a sequence of fixed reflective diffractive optical elements304, 306 and 308 on the face of a rotating prism 300 can have other usesin holographic optical trap methodologies. Similarly, transmissivediffractive optical elements 404, 406, 408 and 410 can be located on theperiphery of a disk 312 and rotated into the beam 100, as shown in FIG.13, or into a reflective optical train in sequence. This also haspotential applications beyond optical peristalsis. In FIG. 13, forexample, each of the diffractive optical elements 404, 406, 408 and 410is rotated into the optical train to project one pattern of the opticalperistalsis sequence.

Static reflective or transmissive diffractive optical elements can befabricated with feature sizes down to the diffraction limit, can haveessentially continuous phase encoding, and thus can implement a widervariety of more complicated trapping patterns than can spatial lightmodulators. Such elements can be produced much more cheaply and do notrequire a computer to operate. The sequence of patterns in such a systemcan be changed by changing the prism or disk of diffractive opticalelements. In this sense, this implementation is less general than thatbased on computer-addressed spatial light modulators.

Because only a small number of precalculated diffractive opticalelements are required to implement optical peristalsis, switchable phasegratings also can be used. The benefits of such an approach include, forexample: freedom from moving parts which can drift out of alignment andwear out, the absence of motors which cause vibration and radiate strayelectric and magnetic fields, reduction in power requirements andimproved compactness.

Encoding high-quality phase holograms on film media will allow opticalperistalsis to be implemented with the equivalent of film loops. Byoffering high-speed cycling through large numbers of diffractive opticalelements, film-based implementations of holographic optical traps willhave applications beyond optical peristalsis.

Optical peristalsis also can be useful for particles and other materialssuch as biological cells which are larger than the physical separationbetween the traps in an optical peristalsis pattern. Similarly,materials such as proteins, DNA, or molecules could also be manipulatedusing optical peristalsis. A large object trapped on a “bed of nails”optical trapping pattern still can be moved by translating the bed ofnails. Rather than defining a single trapping region, however, anoptical peristalsis pattern can establish a large field of trapssuitable for immobilizing a large object wherever it is found. Updatingthe pattern with small displacements, as described above, then willdisplace the entire object. Potential applications include translatingan extended sample into a region where it can undergo tests, rotatingthe object for examination, or controllably deforming the object. Forexample, in the embodiment of FIG. 14, the manifolds 20 of includedoptical traps are shown trapping an extended object 80. Updating thepattern with the manifolds 20 will tend to rotate the extended object80. Similarly, FIG. 15 shows the manifolds 20 of optical traps trappingan extended deformable object 82. The object 82 is more strongly trappedby denser regions of traps, and moving these regions outward insubsequent patterns tends to stretch the object 82.

Each optical peristalsis sequence performs one specific operation. Insome applications, it can be desirable to perform a series of opticalperistalsis operations, with the order of the series perhaps dependingon the outcome of the preceding operations. For example, opticalperistalsis can be used to move a living cell into the center of amicroscope's field of view for reproducible observation. A secondsequence then could be engaged to rotate the cell into a desiredorientation. Then a third sequence can implement a particular test.Based on the outcome of that test, additional optical peristalsissequences can be selected to collect the cell or dispose of it. Each ofthese sequences can be precalculated, thereby removing much of thecomputational burden from the holographic optical trap system.Similarly, different subsequences of optical peristalsis operationscould be incorporated into a single program, wherein a first subsequencecould separate particles into two or more distinct flows, a secondsubsequence could disperse particles from a particular location, a thirdsubsequence could mix two separate streams of particles into a singleflow, a fourth subsequence could concentrate a plurality of particlesinto a particle region, and particles can be “moved” from pattern topattern in a variety of other ways as well. A variety of combinations ofsubsequences such as those described herein could be incorporated into asingle program, and these subsequences could be used sequentially and/orsimultaneously as needed using a variety of types of optical gradientsas described herein. Because very few diffractive optical elements arerequired to implement any one of the sequences, only modest elaborationof the proposed implementations would be needed to select among acollection of available sequences for such multistage operations.

Additionally, it is also possible to practice the present inventionwithout the use of optical traps as conventionally understood to requirespecific optical gradient conditions to hold a particle. For example, aplurality of deterministic optical gradients can be established andincorporated into a plurality of manifolds and patterns as generallydescribed above. These optical deterministic gradients operate to “hold”or restrain, but not necessarily form an optical trap, for individualparticles in a particular position for a sufficient period of time insequence to generate an optical peristalsis effect. In other words,repeatedly cycling through first, second, and third patterns ofdeterministic optical gradients will move individual particles along adesignated path. The optical gradients are deterministic in a sense thatthe conditions that are applied are sufficient to achieve the intendedresult with more than just a mere probability of success.

While preferred embodiments of the invention have been shown anddescribed, it will be clear to those skilled in the art that variouschanges and modifications can be made without departing from theinvention in its broader aspects as set forth in the claims providedhereinafter.

1. A system for manipulating a plurality of particles, comprising: aplurality of beams of laser light, the beams of laser light establishinga plurality of optical traps; a plurality of sequentially spacedpatterns with each of the patterns comprising at least one optical trapformed from at least one of the beams of laser light; and an opticalcomponent sequentially illuminating and extinguishing each of thepatterns using the beams of light at intervals close enough after theextinguishing of the previous pattern enabling capture and transfers ofa particle from one of the patterns to another causing the particle totravel from one of the patterns to the next one of the patterns.